Energy Selective Filter Research Articles

Energy Selective Filter with Power-Dependent Transmission Effectiveness in Waveguide

A novel Energy Selective Filter (ESF) mounted in waveguide is presented based on nonlinear element, which is sensitive to the power intensity of incident wave achieving frequency selection as well as energy selection. The proposed ESF consists of three parts, the middle circuit board with diode loaded, the upper and bottom ground metallic patches. The mechanism of the ESF is analyzed through equivalent circuit model and its performance is investigated numerically and experimentally. According to the waveguide measurement, a shielding effectiveness of 13 dB is achieved in case of high power input and the insertions loss is less than 0.3 dB across the whole frequency range when low power signal inputs. It is a pluggable component in waveguide that could reflect high power signals of specific frequency to protect the following electronic equipment.

Simulations of geometry effects and loss mechanisms affecting the photon collection in photovoltaic fluorescent collectors

Monte-Carlo simulations analyze the photon collection in photovoltaic systems with fluorescent collectors. We compare two collector geometries: the classical setup with solar cells mounted at each collector side and solar cells covering the collector back surface. For small ratios of collector length and thickness, the collection probability of photons is equally high in systems with solar cells mounted on the sides or at the bottom of the collector. We apply a photonic band stop filter acting as an energy selective filter which prevents photons emitted by the dye from leaving the collector. We find that the application of such a filter allows covering only 1% of the collector side or bottom area with solar cells. Furthermore, we compare ideal systems in their radiative limits to systems with included loss mechanisms in the dye, at the mirror, or the photonic filter. Examining loss mechanisms in photovoltaic systems with fluorescent collectors enables us to estimate quality limitations of the used materials and components.

Effects of non-ideal energy selective contacts and experimental carrier cooling rate on the performance of an indium nitride based hot carrier solar cell

The performance of an InN based hot carrier solar cell with a bulk InN absorber has been evaluated using an innovative approach that takes into account absorber energy-momentum dispersion relations, energy conservation, Auger recombination and impact ionization mechanisms simultaneously. The non ideality of the energy selective filters has also been included in the model. In order to obtain practical achievable values of conversion efficiency, the actual thermalisation velocity of hot carriers in InN has been measured using time resolved photoluminescence. Results of the computations shown limiting efficiencies of 24% for 1000 suns and 36.2% for maximal concentration.

Single layer of silicon quantum dots in silicon oxide matrix: Investigation of forming gas hydrogenation on photoluminescence properties and study of the composition of silicon rich oxide layers

Structures consisting of a single layer of silicon quantum dots in a SiO 2 matrix show interesting optoelectronic properties and potential use as energy selective filters, which are a crucial component for the realization of the hot carrier solar cell. In this work single layer silicon quantum dots in SiO 2 have been realized using a magnetron sputtering technique. Quantum dots are formed by annealing of a silicon rich oxide layer deposited between a thermally grown SiO 2 layer and a sputtered SiO 2 layer. The effects of a forming gas post-hydrogenation process on the photoluminescence of the single layer of quantum dots have been investigated in order to understand the photoluminescence mechanism. It was found that for sputtered silicon quantum dots in SiO 2 matrix the photoemission mechanisms are primarily due to quantum confinement and does not strongly rely on matrix defects. In addition, physical and optical properties of several thick silicon rich oxide layers, with different chemical compositions, have been investigated in order to optimize the stoichiometry of silicon rich oxide in the single layers.

Directional selectivity and ultra-light-trapping in solar cells

Directional and energy selective optical surface structures attached to solar cells may result in both, enhancement or deterioration of photovoltaic performance of a solar cell. On the one hand, restricting the cell acceptance to the small incidence angle of direct and circumsolar irradiation enhances the maximum path length of the light in a solar cell with Lambertian surfaces even above the Yablonovitch limit (ultra-light-trapping). On the other hand, restrictions to small acceptance angles imply losses of diffuse sunlight, even for perfectly tracked cells. Using temporally resolved solar irradiation spectra, we simulate the enhancement and loss in the annual energy yield of silicon solar cells of various thicknesses. We assume an idealized angular and energy selective filter on top of the Lambertian surface of the absorber and compare the results to a Lambertian surface only. We find a maximum annual gain in the energy density of 32.5% for 1 μm, and of -10% for 10 μm and 100 μm thick perfectly tracked crystalline silicon solar cells. The simulation implies various tracking modes and two different locations. Finally, we introduce two possible realizations of such a filter; a Rugate stack and inverted opals. In experimental measurements, we could verify the absorptance enhancement by such a structure applied on top of a thin silicon wafer.

Enhanced Light-trapping in Solar Cells by Directional Selective Optical Filters

AbstractDirectional selective optical filters increase the photon confinement of solar cells with a Lambertian light-trapping scheme. These filters restrict the transmission of incoming sunlight to a cone of limited acceptance angle. This paper models the efficiency gain or loss caused by an ideal directional and energy selective filter on top of a solar cell, and compares it to a cell with Lambertian surface and a planar absorber. The enhancement of light trapping by the directional filter is illustrated by the enhancement of the quantum efficiency of normally incident light. Simulations of the annual yield demonstrate that the improved light trapping results in an overall energy gain of more than 10 % for a tracked system.To achieve this gain at the equator,a filter with small acceptance angle of 5 ° that is active below the threshold energy ˜1.5 eV has to used.

Loss Mechanisms in Photovoltaic Fluorescent Collectors

AbstractMonte-Carlo simulations calculate the photon collection of fluorescent collectors in photovoltaic systems. We focus on two collector geometries: solar cells mounted at the collector sides, and solar cells covering the back of the collector. A mirror covers the bare back sides of both systems. On top lies optionally a photonic structure, which acts as an energy selective filter. Ideal systems in their radiative limits are compared to systems where loss mechanisms in the dye, at the mirror, or the filter are included. The examination of loss mechanisms in photovoltaic systems with fluorescent collectors enables us to estimate quality limitations of the used materials and components.

Electron entanglement near a superconductor and bell inequalities

Near the interface between a normal metal and a superconductor, Cooper pairs penetrate into the normal side, giving rise to the proximity effect. The two electrons of these pairs have entangled spin and orbital degrees of freedom. Nonlocal features of quantum mechanics can be probed by separating these two electrons. This is achieved with a fork geometry with two normal leads containing either spin- or energy-selective filters. A signature of entanglement can be detected by measuring the positive noise cross-correlations in this fork. In the case of energy filters, Bell-inequality checks constitute a definite probe of entanglement. We formulate Bell-type inequalities in terms of current-current cross-correlations associated with contacts with varying magnetization orientations. We find maximal violation (as in photons) when a superconductor is the particle source.

Electronic entanglement in the vicinity of a superconductor

A weakly biased normal-metal-superconductor junction is considered as a potential device injecting entangled pairs of quasi-particles into a normal-metal lead. The two-particle states arise from Cooper pairs decaying into the normal lead and are characterized by entangled spin- and orbital degrees of freedom. The separation of the entangled quasi-particles is achieved with a fork geometry and normal leads containing spin- or energy-selective filters. This solid state entangler is characterized by noise cross-correlations which are identical to the noise in one lead, a signature consistent with entanglement. A connection to Bell-type experiments is envisioned (cond-mat/0009193).